Abstract Duchenne muscular dystrophy (DMD) is the commonest lethal inherited X-linked myopathy. The most promising approach to treating this condition, is by use of antisense agents that promote skipping of exons that disrupt open reading frame so as to provide a translatable form of the transcript, thus restoring expression of the missing dystrophin protein. Current clinical trials of this idea have given results that are compromised by low yields of dystrophin and inter-sample variation. This proposal aims to evaluate the fundamental elements of the processes that link exon-skipping to the production and maintenance of functional amounts of dystrophin in muscles. To do this we will investigate the effects of exon-skipping within the mutant dystrophin gene on the production of the 3 different truncated dystrophin proteins produced by skipping different exons and measure the stability and longevity of these proteins within skeletal and cardiac muscles of the dystrophic mdx mouse. We will use the mdx mouse in which exon 52 has been deleted from the dystrophin gene because this mutation presents a number of options for restoring open reading frame and dystrophin production by skipping of different exons that are the main targets of human trials. By use of Mass Spectroscopy techniques recently developed within our laboratory we can accurately measuring the amounts of dystrophin and dystrophin-associated proteins, and will follow the dynamics of their production, stability and turnover. Our aim is to relate these measures to the extent of alleviation of pathology associated with the restoration of 3 different these proteins. This will be the first investigation of the dynamics of this class of muscle proteins in muscles in vivo and will provide methods and protocols that will be more widely applicable. On the basis of this knowledge it should be possible to devise optimal protocols for application of exon-skipping to DMD boys in clinical trials. It will also provide an objective method of selecting the best exons and combinations of exons to skip as the progressively improving antisense reagents become available.